Optical fibers continue to play an ever increasing and important role in communications signal transmission, and are steadily replacing traditional electrical signal transmission means such as coaxial cable and twisted pairs. Optical fibers offer the advantages of a large signal bandwidth coupled with a relatively small size and light weight. These advantages, however, carry with them certain problems inherent in the nature of the optical fiber cable itself For example, the optical fibers used in the cables are primarily made of glass or other low ductility materials and are mechanically fragile, being characterized by a low strain fracture point, especially in tensile loading. As a result, therefore, cable structures have been developed for mechanically protecting the optical fibers in various environments, to include outside installation and cable pulling operations.
One of the structures developed to protect optical fibers has been the inclusion of strength members in the cable. The strength members are not involved in signal transmission, but are instead used to limit the strain on the optical fibers and to carry the load of the optical fiber cable where, for example, the cable is suspended above ground or is being pulled off of a cable reel.
In U.S. Pat. No. 4,844,575 of Kinard et al., there is shown a lightweight optical fiber cable which includes a sheath system having two strength members made of a metallic material diametrically opposed on each side of a cable central core formed from a tubular plastic jacket, in which the optical fibers are carried. The strength members extend longitudinally along and are parallel to the cable axis. The strength members are enclosed in the cable by the plastic jacket, being sufficiently coupled with the jacket to provide a composite cable arrangement with a predetermined relative tensile and compressive stiffness capable of withstanding the expected compressive and tensile loadings.
In U.S. Pat. No. 5,125,063 of Panuska et al., a lightweight optical fiber cable is shown having at least one bundle of optical fibers disposed within a tubular member forming a cable central core enclosed by a sheath system, the sheath system including two elongated longitudinal strength members extending along the axial length of the cable. The sheath system disclosed in Panuska et al, also includes a metallic armor layer which encloses a waterblocking tape for increased tensile and compressive stiffness, as well as, for protection of the optical fiber cable from damage.
An inherent problem in the use of metallic strength members, however, arises when the cable is struck by lightning so that an unexpected and decidedly unwanted electrical charge travels along one or both of the strength members forming a part of the cable. Moreover, a lighting strike may also penetrate the cable jacket and bum through to a metallic oversheath and/or the metallic sheath of the cable, transmitting electricity along the length of the cable until the electrical current is either dissipated by grounding, or is otherwise shorted out. It is also possible that due to ambient conditions, the cable may hold a static electrical charge in either of the strength elements or the metallic sheath(s). Grounding the cable is thus necessary in order to prevent damage to people and property from stray and unexpected electrical current passing through the mechanical components of the cable, or from any static charges in the cable.
As a consequence, optical fiber cable is routinely grounded every time it is spliced, and especially where the cable enters into a commercial or residential structure. This is accomplished through the use of conventional bonding and grounding hardware known to those skilled in the art.
In the known bonding and grounding hardware a sealing clamp is passed over the outside of the cable and the plastic cable jacket is then cut and opened to leave a portion of the metallic sheath and the metallic strength members exposed. The metallic strength members are then bent at an angle of approximately 90.degree. from the longitudinal axis of the cable, and the base section of the grounding block is placed over the cable. The bent portions of the metallic strength members fit within notches formed in the base of the grounding block, and the sealing clamp is slid over the base of the grounding block and tightened to secure the grounding block to the cable. Any excess portion of the metallic members protruding beyond the base of the grounding block is then cut. A bond shoe is then slid between the corrugated metal sheath and the tubular member of the optical fiber cable until a threaded bond shoe stud positioned on the bond shoe lies against the end of the metallic sheath, the bond shoe stud being generally aligned with the grounding block. A bond plate is then placed over the bond shoe, so that the bond shoe stud extends upward from the bond shoe and is passed through an opening in the bond plate. A second opening in the bond plate is aligned with a corresponding opening formed in the grounding block so that a threaded fastener can be passed therethrough and into a bonding block which acts to secure the grounding block, the bond shoe, and the bond plate to the optical fiber cable. Thereafter, a ground wire, or ground wires, provided by a cable installer or splicer is placed into the bonding block and secured thereto by set screws, thus grounding the cable.
Although this known type of bonding and grounding hardware can satisfactorily function as grounding means for a cable, from the foregoing it can be seen that it has a large number of individual parts susceptible to being lost or misplaced at the job site, and it is equally apparent that it also takes a great deal of time and effort to perform the required steps to assemble this hardware. In as much as this operation is performed several hundreds of thousands of times per year by cable splicers and technicians, generally working in crowded spaces, the amount of time required to install the known grounding hardware is quite significant. It thus follows, as with any other labor intensive operation, that the labor costs incurred to perform this work are equally as significant a factor when measuring the costs to perform cable grounding operations. Thus a savings of time of even only a few minutes per installation will result in a very significant cost savings over the course of a year.
What is needed and is not seemingly available in the art is an improved, ie. simplified, universal grounding clip which requires little on-site assembly, and which is quickly and easily used to minimize the time needed, and thus labor costs, to ground the metallic strength elements and/or metallic sheaths of a cable. Desirably, such a grounding clip should have relatively few components or parts to minimize the material costs of the grounding clip, as well as the labor costs of handling and installing the grounding clip not to mention minimizing the possible loss of parts.